<b>To view all items in this collection click on the title tab in search box above</b><br><br>These investigations are a compilation of various nationally important scientific findings, covering topics such as inshore species, stock assessments, advances in techniques for developing management advice and reports on fishing surveys conducted.


Irish Fisheries Investigations

Recent Submissions

  • Application of EDA (v 2.0) to Ireland: prediction of silver eel Anguilla anguilla escapement

    de Eyto, E.; Briand, C.; Poole, R.; O'Leary, C.; Kelly, F. (Marine Institute, 2016)
    Eel Density Analysis (EDA) is a modelling framework that can be used to estimate eel populations in aquatic habitats. Survey data (primarily electrofishing operations) are used to build predictive models describing the presence/absence and the density of eel. These models are then applied to the entire network of aquatic habitat in the area of interest to estimate the total population size. The fluvial (riverine) population of yellow eel in Ireland was estimated using the EDA (v2.0) model (Jouanin et al., 2012). A total fluvial population of 8,032,834 yellow eels and 200,821 silver eels (using a silvering rate of 2.5%) was estimated for 2011. Eel presence and abundance decreased as the distance to the sea increased, and the percentage of calcareous geology in the catchments decreased. Stock indictors (B0, Bbest and Bcurrent) were calculated from these yellow eel estimates to enable the display of precautionary diagrams for each EMU in Ireland. Lake production was also calculated for 2011, using empirical data from a small number of catchments. A precautionary diagram for this total production (fluvial and lacustrine habitat) is presented, and compared with previous estimates of stock indicators for Ireland.
  • Sediment characteristics and local hydrodynamics and their influence on the population of Nephrops around Ireland

    O'Sullivan, David; Lordan, Colm; Doyle, Jennifer; Berry, Alan; Lyons, Kieran (Marine Institute, 2014)
    The Norway lobster, Nephrops norvegicus, is the second most valuable commercial spe-cies landed from Irish waters. The species is dependent on muddy seabed sediment in which burrows are constructed. Larvae are hatched from the seabed into the water column. The distribution of Nephrops depends in part to the presence of suitable sediment and also from larval supply modulated by existing local hydrodynamic regimes. The pelagic stage of the life-cycle is governed by both physical and biological factors including temperature, water speed and larval maturation rate. This study encompasses three aims, 1: to synthesise available sediment data and examine the spatial extent of potential Nephrops habitat in waters around Ireland, 2: investigate local hydrodynamic conditions on Nephrops fishing grounds which are likely to be encountered by planktonic larvae following hatching and 3: to employ a particle tracking model to study the potential dispersal fields of Nephrops larvae from individual fishing grounds and assess stock connectivity. The study finds that larval distribution between fishing grounds is dependent on variable seasonal conditions, the geographical size of an area and its proximity to other grounds. Fishing grounds in the Irish Sea and Porcupine Bank are isolated from other areas, whereas grounds in the Celtic Sea exhibit a high degree of connectivity and should be considered as a meta-population. Successful annual recruitment to the adult population of this species is largely dependent on favourable environmental conditions which enable the re-seeding of the same or adjacent grounds.
  • The Status and Management of Oyster (Ostrea edulis) in Ireland

    Tully, O.; Clarke, S. (Marine Institute, 2012)
    Fourteen oyster surveys were completed during 2010-2012 in 6 bays on the west coast of Ireland prior to and following annual late autumn fisheries. Vessel based surveys using locally designed dredges were undertaken using in Tralee Bay, Galway Bay, Kilkieran Bay, Clew Bay, Blacksod Bay and L. Swilly. Survey extent was defined by local knowledge of the distribution of beds in each bay and from previous survey reports. The extent of oyster beds, oyster densities, biomass, size composition and growth and mortality rates are reported. The governance and management of oyster fisheries in Ireland is described and conservation requirements for oyster habitat are discussed with reference to the EU Habitats Directive. Survey extents varied from 0.9-13km2. Population densities of oyster were generally <0.5 oysters m-2 but higher densities of up to 50 oysters m-2 occurred in areas of inner Tralee Bay. In other sites, densities did not exceed 5 oysters m-2. The majority of national oyster biomass occurred in inner Tralee Bay where biomass varied from 980-1330 tonnes in the 2010-12 surveys. Biomass in outer Tralee Bay and L. Swilly was approximately 100 and 124 tonnes, respectively. Biomass estimates in inner Galway Bay, Kilkieran Bay, Clew Bay and Blacksod Bay were all less than 50 tonnes. vonBertalanffy growth parameters, k and to, were 0.21year-1 and 0.23years respectively. These parameters were estimated from shell height frequency data and by fixing Linf at 120mm, based on the maximum size of oysters recovered during surveys. Total mortality rates (Z) were estimated from the linear portion of length converted catch curves using these derived growth parameters. Z estimates, in pre and post fishery surveys, averaged 1.07 and 1.30 respectively in 2010 and 0.94 and 1.55 respectively in 2011. Fishing mortality rate (F), derived from the difference in Z estimates in pre and post fishery surveys in inner Tralee Bay, was 0.9 representing an annual removal of 60% of oysters recruited to the fishery. Increase in biomass of a single cohort, simulated using derived growth rate parameters, the size weight relationship and different rates of natural mortality (M) suggests that maximum biomass develops prior to the minimum landing size of 76mm if M>0.4. Improved, site specific, estimates of growth and mortality rates and size at maturity data are needed to provide fisheries management advice for native oysters. Pacific oyster (Crassostrea gigas) was abundant and widespread, in what was previously Ostrea habitat, in L. Swilly. In some of these areas, Pacific oyster was the only oyster species present. In other areas both species co-existed although they were spatially segregated to a degree in relation to shore level.
  • A History of common carp Cyprinus carpio (L.) in Ireland: A Review

    Brazier, B.; Caffrey, J. M.; Cross, T. F.; Chapman, D. V. (Marine Institute, 2012)
    This paper represents the most comprehensive and detailed summary of the history of common carp Cyprinus carpio (L.) in Ireland to date. It charts the earliest known introductions of the species to Irish waters, the rise in popularity of recreational angling for the species from c. 1950 onwards, the work carried out to establish the species in Ireland and explains the primary causes of their more recent distribution increase. Much of the historical research material gathered on common carp in Irish waters, including the first recorded details of introduction, is presented here for the first time.
  • The Maharees spider crab Maja squinado fishery in 2000

    Fahy, E. (Marine Institute, 2001)
    A pot fishery directed on spider crab (Maja squinado) grew out of a mixed tangle net and pot fishery for large crustaceans in the early 1980s. Approximately twenty half decked vessels of 10m in length have been involved for the duration of the fishery but the numbers of pots per vessel has increased; currently 10,000 pots are set for spider crab in Tralee and Brandon Bays during the summer months. Cpue rose initially during the early years of the fishery, then it stabilised and declined although in the late 1990s it again recovered somewhat. Sampling in 2000 suggests that the size composition of the catch has altered since the early years of the fishery, its main consequence being the removal of the older age groups so that the landings now consist almost entirely of a single year class. Aspects of the biology of the Maja squinado are compared with what is already known of the species and a number of recommendations are made for the future management of the fishery. These include a further increase in the size limit, a ban on tangle nets and a cap on fishing effort.
  • Population dynamics, age, growth and maturity of lemon sole Microstomus kitt (Walbaum 1792) sampled between 2000-2002 off the west coast of Ireland.

    King, P. A.; Hannan, J. F.; McGrath, D.; Veldon, M. (Marine Institute, 2006)
    The age, growth, maturity and population dynamics of lemon sale (Microstomus kin), from commercial catches off the west coast of Ireland (ICES division Vllb), was determined for the period November 2000 to February 2002. The maximum age recorded was 14 years. Males of the population were dominated by 4 year olds, while females were dominated by 5 year olds. Females dominated the sex ratio in the overall sample, by month sampled, by age class and by size (from 22cm in total length onwards. when N > 20). Mature male and female lemon sale were encountered at age 2 and above. Von Bertalanffy growth parameters were estimated using the method of Rafail (1973). In recent years, the lemon sale has exhibited a smaller asymptotic length (L∞ = 34.47cm), faster growth rate (K = 0.1955) and younger age at first maturity than in the same area in 1978-1979. These changes are indicative of a decrease in population size following exploitation.
  • The distribution and abundance of cephalopod species caught during demersal trawl surveys west of Ireland and in the Celtic Sea

    Lordan, C.; Warnes, S.; Cross, T. F.; Burnell, G. M. (Marine Institute, 2001)
    Distributional and abundance data on seventeen cephalopod species from three demersal trawl series are presented. Data from one the CEFAS March Celtic Sea Groundfish Survey cover the years 1994-1998 inclusive and a depth range of 57-580 m. Data from two Marine Institute surveys was for October-November 1997 only. One of these surveys was west and south west of Ireland between depths of 27-328 m, the other was conducted in deepwater (520-1174 m) to the northwest. Eleven cephalopod species were caught (14,981 individual cephalopods) during the five CEFAS surveys. Spatial and bathymetric distribution data are presented for the species caught and the interannual variability is discussed. The most numerous species in catches was Loligo forbesi (n = 6,803), however, the highest biomass caught was Illex coindetii (418.3kg). Alloteuthis subulata were common close to shore in water depth of less than 75 m. Swept area density estimates are reported for the most abundant species in catches. Ten cephalopod species were caught during the Marine Institute west coast groundfish survey (774 specimens were examined out of an estimated 8,712 caught). The results show broadly similar patterns in species composition, distribution and abundance to the CEFAS survey. Todaropsis eblanae was the second most numerous species in the survey. Only six cephalopod species (n =196) were caught in the Marine Institute deepwater trawl survey. Todarodes sagittatus was the most common species caught. Deepwater octopods including Benthoctopus piscatorum, Benthoctopus ergasticus and Opisthoteuthis massyae were also caught. This chapter provides a base line of data on cephalopod species which are caught in trawl surveys west of Ireland and in the Celtic Sea.
  • A review of potential techniques to reduce the environmental impact of demersal trawls

    Linnane, A.; Ball, B.; Munday, B.; Van Marlen, B.; Bergman, M.; Fonteyne, R. (Marine Institute, 2007)
    Concern over the possible effects of trawls on the seabed has existed almost as long as the fishing method itself, with early concerns being voiced by fishermen themselves as far back as the 14th century. With the advance in technological developments of trawling gears (i.e. weight and size), particularly over the latter part of this century, the increase in the number of fishing vessels, engine power etc., these concerns are increasingly gaining international public and political importance. This review is divided into two sections. Section 1 gives an overview of the physical and biological effects of bottom trawling and section 2 gives an overview of potential gear modifications.
  • A second assessment of the whelk fishery Buccinum undatum in the southwest Irish Sea with particular reference to its history of management by size limit

    Fahy, E.; Masterson, E.; Swords, D.; Forrest, N. (Marine Institute, 2000)
    Whelk landings in the southwest Irish Sea increased from 56 t in 1990 to 6,575 t in 1996 after which they stabilized between 3,600 and 4,600 t annually. At its peak the fishery supported approximately 80 vessels but this number has halved since. In 1994 a size limit of 50 mm was introduced for conservation purposes. Age based assessments of the landings were carried out in 1994, 1996, 1997 and 1999, for which purpose the fishery, ranging from 52º10’ to 53º30’, is divided into four sectors. Landings to the four sectors display biological characteristics which indicate the occurrence of a number of stocklets rather than a single stock unit. Whelk in the south west Irish Sea are relatively thin shelled and the fishery has a low density of large crustacean predators. There is no evidence of contamination by TBT. The northern and southern ends of the fishery have relatively lower densities of larger/older animals; the centre sectors have smaller whelk of shorter life span at higher densities, some of them showing symptoms of a Lee phenomenon and slower growth. A survey of cpue places heaviest densities on the Codling and Rusk Banks, in strong tidal currents, at depths of < 20 m. Growth and maturation rates vary among stocklets. L∞ ranges from 102 to 116 mm. Length at 50% male maturation is usually within the range of 63 – 68 mm and ages of 6.1-7.2 years although landings to one sector have a 50% male maturation rate of 83 mm and 8.5 years of age. The existing size limit of 50 mm would, at best, afford protection to 40% of spawning males. Compliance with the size limit has been poor. From 20 to 33% of total landings in any of the assessed years have been less than the legal limit and in 1994 51% of landings in one sector were below the acceptable size. Trends in cpue have been monitored since 1990 and some areas do not show any marked tendency. On the contrary, some fishermen in the centre sectors improved their yield between 1994 and 1998. There are two explanations for this: the movement of pots onto virgin ground and the fact that fewer fishermen are competing for landings in the same areas. Whelk have responded to a reduction in fishing effort since 1996 immediately following which mortality coefficients (Z) were highest (0.79); they declined to an average 0.61 in 1999. In terms of yield per recruit however they remain high. The southern sector of the fishery is regarded as being most depleted although very few subsize limit whelks were caught there. The survival of the whelk fishery in the southwest Irish Sea is attributed to the instability of the market which is dominated by a single customer, South Korea. A more effective size limit for this fishery would be 68mm (83 mm in the northern sector) and this is considered unrealistic, suggesting that alternative management measures will have to be considered.
  • Observations on the status of bass Dicentrarchus Labrax stocks in Ireland in the late 1990s

    Fahy, E.; Forrest, N.; Shaw, U.; Green, P. (Marine Institute, 2000)
    Investigative work was undertaken in 1996 to ascertain the strength of sea bass stocks following the introduction of a range of conservation measures which effectively extinguished the legitimate commercial fishery for the species. Information was sought from two sources: estimation of the age composition of the samples and the growth of bass by examining scales from exploited fish. An estimate of the density of juvenile pre-recruit bass was made from a seine net survey undertaken in various estuaries along the south coast. Scales sent in by anglers and obtained through the regional boards from illegally netted fish indicate that a high proportion of bass landed between 1996 and 1998 belonged to the 1989-year class, which had been reported to be exceptionally large in Britain. Back-calculations of length-at-age from the scales of these and seine-netted bass suggested that growth improved in the later 1980s in response to higher sea temperatures but has since declined. Work on an index of juvenile abundance began with 59 seine net hauls made in August 1996 and 1997. On these the areas most likely to support bass were characterised; O-group bass were encountered more frequently than any other age group. Sites most likely to support bass were mud flats overlaid with shallow and still water which had a salinity range of 17 to 22% and bass were associated with certain species of estuarine fish and crustaceans; bass were negatively associated with other species occupying the deeper and more sandy parts of estuaries. Sampling stations for O-group bass have been selected in Youghal Harbour and Wexford Harbour. Further exploratory work is required to extend the list of stations. It was concluded that there has been a temporary increase in the numbers of sea bass, as has been reported by fishermen in Ireland, as a result of more favourable temperatures in the late 1980s. Growing conditions appeared to have deteriorated in the later 1990s and the summer growth ofO-group bass was the weakest in 1999 over the 4 years investigated. A time series of O-group abundance is too brief to permit any conclusions to be reached. However, it can be stated that the recorded densities of juvenile bass between 1996 and 1999 were sparser than would be expected in south east Ireland in view of the supposed heavy winter concentrations of the species in the Celtic Sea.
  • The strategic importance of the fishing sector to rural communities and Ireland: a case study of the Rossaveal Region, Co. Galway

    Meredith, D. (Marine Institute, 1999)
    Fishing and ancillary industries are commonly perceived to be of significant social and economic value by virtue of their geographic location. Past socio-economic studies of fisheries and related industries largely confined themselves to analysing demographic statistics and relating these to official port fish landings data and descriptions of processing and ancillary industries. Despite these efforts, a clear picture of why and how fisheries are of socio-economic significance has not yet been achieved. As a consequence there is little de-tailed understanding of how ecological, legislative and market related changes impact on fisheries dependent communities. This study of the Rossaveal Region was funded by Marine Institute in an attempt to assess the importance of demersal, shellfish and pelagic fisheries to peripheral Irish communities.
  • The state of stocks of cod, whiting, sole and plaice on the west and southwest coasts of Ireland

    Wheatley, S. B.; Connolly, P. L.; Woods, F.; Keatinge, M.; Doherty, M. (Marine Institute, 1999)
    Stocks of cod, whiting, plaice and sole in ICES Divisions VIIb,c and VIIj,k are an important part of the Irish fishing resource yet, until 1993, were not subject to any assessment. Landings of these stocks in 1996 were valued at £8.6 million, representing 17% of the overall value of all Irish landings of demersal species. In 1993, the Fisheries Research Centre initiated a stock monitoring programme with the aim of providing adequate data to enable an assessment of these stocks. This paper presents the results of growth, catch curve and yield per recruit analyses from the monitoring programme conducted between 1993 and 1996. Preliminary results show that all of these stocks but sole in VIIb,c are over-exploited. TAC levels (based on reported catches in previous years) may be inappropriate for the current stock sizes. It is also important to compare biological characteristics between ICES Divisions to determine the appropriate assessment areas. Comparisons of biological parameters between areas have so far been inconclusive.
  • Marine fauna of county Wexford, Ireland: The fauna of rocky shores and sandy beaches

    Healy, B.; McGrath, D. (Marine Institute, 1998)
    Information accumulated during 20 years of investigations on the coast of County Wexford is summarised. Topics include shore descriptions, faunal records, transectal surveys on rocky shores and sandy beaches, cryptofaunal studies on rocky shores, and ecology, reproduction and population dynamics of many of the dominant species. Studies were mainly carried out on exposed and sheltered rocky shores in the region of Camsore Point, Forlorn Point and Hook Head, and sandy beaches at Kilmore Quay, Camsore, Came, Rosslare Harbour and Rosslare Point, but some collections were made in a wide range of habitats throughout the county. A total of 484 taxa were recorded. Carnsore is the type locality for four species of oligochaete and two more are yet to be described. The fauna lacks some of the elements of west Irish coasts but is richer than on the mid-eastern coast owing to the presence of southern species. Differences in species abundance and population structure on south and east coasts are described, and possible reasons for the differences are discussed.
  • The commercial exploitation of shrimp Palaemon serratus (Pennant) in Ireland

    Fahy, E.; Gleeson, P. (Marine Institute, 1996)
    Palaemon serratus is at the northern limit of its range in the British Isles. In Ireland it is most abundant in the southwest where it has been commercially fished since the mid-1970s. Landings in recent years have averaged between 200 and300 tonnes annually with an estimated export value of £2—3 m. These landings represent a three-fold expansion over those of the previous decade. The biology of the species was investigated over a 12 month period in Bantry Bay using commercial gear. At most times of the year there is a bimodal length frequency distribution and the life expectancy is interpreted as 2 years. Condition factor does not vary much during the year in males and immature females but the larger females put on up to 30% weight in the autumn. The reproductive cycle in Bantry resembles that in the south of England rather than that in north Wales, these two locations providing earlier studies of the species. The largest females come into berry in October and egg carriage within the population continues into the following summer; in May, a second group of smaller females, belonging to the 0 age group, carries eggs. Corroborative evidence for this interpretation is provided by the size of the ova and their developmental state. There would appear to be an influx of shrimp to Bantry Bay which builds up from May and declines after January but cohort and gender migrations are unclear. Catch per unit of fishing effort (cpue) is estimated from the weight of a consignment of shrimp delivered to a processor. Such data are variable but they are also consistent and stable over the short-term and throughout the range of shrimp fisheries. A time series from 1977 to 1994 suggests a 36% decline; the significance of this is not known. Shrimp fishing takes place during the autumn and winter months. In the southeast landings are taken throughout the year but those outside the period August to January, inclusive, do not exceed 8% of the total. In the southwest only 3% of landings are made outside these months, while in Connemara none was reported Mechanical grading in the factory is explored as a means of reconstructing age profiles. Two patterns of exploitation are described: that of the southwest and southern coast has a larger proportion of 0 group shrimp which may reach 40% by numbers of the total landings; in Connemara the proportion of 0 group shrimp is much smaller. Attempts are made to find some method of predicting aspects of the catch from biological and sea temperature data. There is a suggestion that a large brood year is influential in producing a successor whose size is estimated 2 years later. The sustainability of the shrimp fishery is unknown and two precautionary measures are suggested as the basis of a management regime: enlarging the mesh size to improve the exploitation pattern and limiting the fishing season.
  • The abundance of boarfish (Capros aper) along the western shelf estimated using hydro-acoustics

    O'Donnell, C.; Farrell, E.; Saunders, R.; Campbell, A. (Marine Institute, 2012)
    The Boarfish (Capros aper, Linnaeus) is a relatively small deep bodied fish growing up to 23 cm in total length. Typically reddish in colour with large eyes and a highly protrusible mouth boarfish are known to inhabit shallow shelf seas to shelf slopes from 40-600 m. Boarfish are a mesopelagic shoaling species distributed in the eastern Atlantic from Norway to Senegal including the Mediterranean. Exploratory fishing for boarfish by Irish vessels began in the later 1980s when commercial quantities were encountered during the spring horse mackerel (Trachurus trachurus) and mackerel (Scrombrus scomber) fishery in northern Biscay. During the early 2000s the Irish landings were relatively small (<700 t per yr) and it was not until 2006 that a directed fishery developed in earnest. Landings peaked in 2010 at over 137,000 t prior to the introduction of TAC control and interim management plan. This survey represents the first dedicated exploratory acoustic survey for boarfish (Capros aper) undertaken along the western seaboard of Ireland. The survey was timed to coincide with peak spawning time as determined from histological analysis of commercial catch samples. Area coverage was based on the distribution of catches from the IBTS survey time series and from catch data from the pelagic fleet targeting boarfish since 2005. In total 3,160 nmi (nautical miles) of cruise track was undertaken by the MFV Felucca, over 32 transects relating to an area coverage of over 89,500 nmi². Coverage extended from the 50 m contour to the shelf slope (250 m). Transect spacing was set at 15 nmi throughout to make best use of the time available and the large geographical area to be covered. The results presented here are a composite of data collected during this survey and on the northwest herring survey (RV Celtic Explorer). Both surveys were timed to link up and were carried out over 33 days from north (59°N) to south (47°30’N). Acoustic data were collected using a Simrad EK 60 scientific echosounder via a Simrad ES-38B (38 KHz) split-beam transducer which was mounted within a tow-body. This configuration was calibrated on the survey vessel prior to departure. An age length key (ALK) compiled primarily from commercial samples collected during 2010 was applied during the analysis of survey data. Age distribution indicate that the stock was dominated by the following age classes in terms of abundance: 6, 7, 20+ and 9 year old fish and 20+, 9, 7 and 10 years in terms of biomass respectively. Immature fish from 0-2 years were poorly represented in survey catches and this is consistent with a spawning movement of mature stock away from feeding grounds on the shelf. During the survey boarfish shoals were primarily distributed along the shelf edge occurring as aggregations actively spawning or in a state of near readiness to spawn. As a result the abundance estimate is almost exclusively composed of mature individuals (>99%) which is in contrast to the primarily on-shelf distribution of commercial catches. The biomass and abundance estimates presented here were calculated using a modelled TS-length relationship, from as yet unpublished data for boarfish and applied retrospectively to acoustic data.
  • Distribution, population structure, growth and reproduction of the razor clam Ensis arcuatus (Jeffreys) (Solenaceae) in coastal waters of western Ireland

    Fahy, E.; Norman, M.; Browne, R.; Roantree, V.; Pfeiffer, N.; Stokes, D.; Carroll, J.; Hannaffy, O. (Marine Institute, 2001)
    Samples of razor clams, Ensis arcuatus, the species which makes up the majority of landings from the west coast of Ireland, were collected by commercial fishery methods, in association with the dredge fishery and by scuba diving, from three locations off the coast of Co Galway. E. arcuatus occupies coarse sand (of maerl and shell fragments) and rarely co-exists with the other common species of the region, E. siliqua. E. arcuatus were aged, an age-length-key devised for them, and growth parameters (Linf, k and t0) were calculated. Their maturation state was established by histological examination. Evidence suggests that Ensis arcuatus is mainly a spring spawner, although some spawning appears to take place in most months, with a spatfall in June/July. Maturation commences in its third year. Asymptotic length is achieved at 10 years, approximately, and there was little variability in growth among the three sampling areas or between the sexes. In a small bed of razor clams in Cill Chiarain Bay, Co Galway, there would appear to have been a spatfall in most, if not all, of the past 15 years. The quantitative distribution of E. arcuatus in a single bay within the boundaries of Comharchuman Sliogeisc Chonamara Teo, Co Galway, was estimated by divers salting quadrats of 0.33 m2. The razor clam community is divided into a generally distributed fraction occurring at low density (described as the non-bed) and at a relatively higher density (described as the clam bed). The bed was situated in the lee of reefs, which is usually the case for this species along the Atlantic seaboard. More than 90% of the biomass was above the E.U. minimum size limit.
  • The inshore pot fishery for brown crab (Cancer pagurus) landing into south east Ireland: estimate of yield and assessment of status

    Fahy, E.; Carroll, J.; Stokes, D. (Marine Institute, 2002)
    Although it is regarded as an important focus of brown crab Cancer pagurus landings, the fishery in south east Ireland is poorly documented and the official statistics are believed to under-record the species by a factor of 2-3. This appraisal of the south east Ireland brown crab fishery is based on >22,000 records of sales transactions from the 1990s and a comparison of the biological characteristics of landings in the late 1960s with thirty years later, in the context of increasing fishing effort. The three buyers who gave access to their books inwards for periods of the 1990s, purchase from the same fishing community and they compete for product but they occupy slightly different market niches: a vivier truck operator exports to Spain, a processor concentrates on autumn purchases of female crab for vacuum packing while the third buys crab claws for human consumption and crab bodies which are used as bait for whelk Buccinum undatum. Only the first sales of crab from 55 km of coastline are considered. In this area fishing effort doubled between 1972 and 1988 but expansion accelerated in the following decade by at least 128%; a single operator increased his effort by 80% between 1988 and 1998. In the 30 years after 1968, the number of pots per km of coastline rose by 241%.The sale of brown crab is recorded in consignments which are raised to live weights in the analysis. Consignment size fell steeply in the late 1980s and early 1990s after which it stabilised; adjusting the figures to allow for increasing effort accentuated the trend; at the same time consignment number rose. Allowing that a decline in consignment size was accompanied by an increase in pot number, consignment number should have risen by 310% to maintain landings at the level recorded in 1990; the largest recorded increase in consignment number was by 230% and while it is accepted that all sales transactions have not been obtained, it is likely that LPUE has been declining over the 1990s in real terms in this fishery. Increasing fishing effort during that time is seen as a product of better technology, stimulated by a desire to compensate for falling LPUE. Comparison of size and sex composition of the landings recorded in the late 1960s and the late 1990s are inconclusive. Depth of water and type of substratum are likely to influence the composition of inshore landings. An argument is presented that the south east inshore crab fishery is fully or over-exploited. It is likely to have an offshore component and such occasional data as are available on brown crab further south suggest that the offshore is an under-exploited fishery. In which case, the rate of interchange between the two components is likely to be crucial to the continued performance of the inshore fishery
  • Bionomics of brown crab Cancer pagurus in the south east Ireland inshore fishery

    Fahy, E.; Hickey, J.; Perella, N.; Hervas, A.; Carroll, J.; Andray, C. (Marine Institute, 2004)
    The south east inshore brown crab fishery is delimited by the boundary of longitude - 6.3, within a coastal band of approximately 18 km (10 nm) in width and it extends along the south coast of Co Wexford for a distance of approximately 55 km; evidence for the stock extending into the inshore fishery west of the Waterford Harbour estuary is sparse. The fishery, whose maximum extent is calculated at 427 km2, yielded up to 700 t per year during the 1990s. In 2002 annual landings of 959 t accounted for 8.2 % of the national catch. The average overall LPUE was 0.87 kg per pot lifted in that year. Brown crab were landed whole or as claws, for human consumption, and clawed or, of poorer quality, with claws, to provide bait for the whelk fishery. This fishery is not considered to have any discard of legally sized crab and, in consequence, a large percentage of the landings is poorly conditioned. The stock is intensively fished; the amount of gear in use increased almost 5 fold since the mid 1970s. Landings per boat declined since the late 1980s although this may be as a result of sharing among a greater number of vessels. In 2002 an estimated 60 - 69 vessels fished brown crab in the peak autumn months. In 2002 and early 2003, 3,674 crabs were tagged in the inshore fishery; of these 14.4% were recaptured (12.8% of tagged females and 20.7% of tagged males). Observations made during tagging operations in 2002 only were used to clarify sex ratio and the incidence of recently moulted animals. The crab stock consists of a migratory female component which moves into shallow waters during the summer months probably to moult and mate. The male component is more sedentary. Both sexes move at speeds which slow during the summer months and increase again as the year advances; maximum speeds of 2 km/day were recorded for both sexes in the autumn. Movements by male crab were random while females adopted a south west trajectory. The greatest distance recorded for a tagged female crab was 136 km after 287 days at liberty. Other tagged females, reported by French vessels, were recaptured in ICES division VIIg which may be the over-wintering area for the stock. These animals had moved between 69 and 75 km from their release point. Tag reporting by the industry is considered to have been low. Based on the 'rate of tag recovery, the estimated rate of exploitation was lower than expected in an intensely fished stock. Population estimates were attempted using the Petersen formula and on the basis of assumptions about mortalities which recognized the phenomena of moulting and migration. The south east crab stock moves with the current which is westerly along the southern Irish coast. Recorded migrations were also short when compared with those of brown crab in the northern stock and in several other documented fisheries. The Nymphe Bank which adjoins the south east fishery has a water current pattern which retains larvae and it is known to have a high density of brown crab in the plankton. The existence of retaining currents may make the kind of long migrations which characterise others unnecessary for this stock. The status of the south east fishery is not known. LPUE indices provided by the Roscoff super-crabber fleet for ICES statistical division VIIg remained fairly stable between 1987 and 2002 but the quantity of crab captured by those vessels has declined considerably in most years since 1995.
  • Larval distribution of commercial fish species in waters around Ireland

    Dransfeld, L.; Dwane, O.; McCarney, C.; Kelly, C. J.; Danilowicz, B. S.; Fives, J.M. (Marine Institute, 2004)
    In April 2000 a base line survey was conducted on the larval distribution of commercial fish species off the west, north and south coasts of Ireland. Ichthyoplankton samples and in situ CTD data were collected, whilst simultaneously capturing remote sensing images of chlorophyll and sea surface temperatures. The survey sampling area covered the Celtic Sea from the Irish south coast to 49 degree N, the western shelf including the Porcupine Bank and the northern shelf up to the Stanton Bank. The sample grid design was based on the international mackerel & horse mackerel egg survey with station spacings of 0.5 degree latitude and 0.5 degree longitude. Ichthyoplankton samples were collected with a Gulf III plankton sampler, which was deployed on oblique tows from the surface to within 5 metres of the bottom (200m max). A self-logging CTD sensor (Promonitor) was attached to the Gulf and recorded depth, temperature and salinity profiles for each deployment. Results from the Promonitor CTD showed that strong temperature and salinity gradients were encountered during the survey. Lowest temperatures coincided with lowest salinity in the North Channel of the Irish Sea while highest salinities and temperatures were found to the south west of Ireland.Thermal fronts were found in the eastern Celtic Sea and on the north west coast of Ireland.The AVHRR images showed a progressive increase in surface temperatures in the Celtic Sea and west of Ireland. Highest surface chlorophyll concentrations were associated with cooler less saline water in the Irish Sea and the coastal areas around Ireland. In the western Celtic Sea surface chlorophyll concentrations increased as the survey progressed to form a phytoplankton bloom towards the end of the survey. Larvae of interest showed distinct distribution patterns, with some species being confined to particular areas or spawning grounds while others were spread over the whole survey area. The survey identified two important larval hotspots: Cod larvae were concentrated in the eastern Celtic Sea, where other gadoid species such as haddock, whiting, pollack and saithe were also found in high numbers.This area is associated with the Celtic Sea front and shows increased primary productivity, which could present a favourable environment for successful larval survival. Stations in the southwest of Ireland sustained high concentrations of hake, megrim and mackerel larvae. The waters with high numbers of these three species stretched from shallow inshore stations to deeper ones along the continental shelf and were characterised by high temperatures and salinities. SeaWIFS satellite images suggest the formation of a phytoplankton bloom within this larval hotspot, which would provide the necessary resources for successful larval growth.
  • The Dundalk Cockle Cerastoderma edule Fishery in 2003-2004

    Fahy, E.; Carroll, J.; Murran, S. (Marine Institute, 2005)
    A cockle fishery in Dundalk Bay has been infrequently documented since 1970. Cockle bearing sands and muds are 44.5 km2 in extent. The bay, which is in an SPA and a cSAC also supports large numbers of overwintering birds, of particular relevance is the oystercatcher (Haematopus ostralegus). In 2003 and 2004 when an assessment of the fishery was undertaken, cockles ranged from 0 to 8+ years of age, but the vast majority were 0 and 1+ animals. Growth was rapid and 53% of asymptotic length (49.1 mm) was achieved at the first winter. In agreement with observations elsewhere, the density of the rapidly growing animals was very low. The estimated cockle biomass in spring 2004 was 1,654 tonnes comprising 143 million animals. A survey undertaken in spring 2004, suggested that spat falls contributing to the population may not have been evenly distributed throughout the Bay. Condition factor in 2003 and 2004 did not conform to an expected seasonal pattern, suggesting that some parts of the area supported better growth rates than others. Cockle landings from this fishery are of good quality. Cockle size is at the upper end of the range in Britain and Ireland and the majority of individuals landed by suction dredging were 1+ years old. Raked landings contained more 2+ cockles than suction-dredged ones. Damage to cockles discarded by suction dredging followed the pattern reported elsewhere and damage rates increased with the size of the animals. Some cockle landings have probably always been made in Dundalk Bay by picking and raking, but 2001 marked the beginning of an expansion of the dredge fishery, whose landings exceeded 200 tonnes in 2004. The necessity for controls and management of this fishery in the context of EU legislation and particularly within the constraints of the Habitats Directive is briefly examined.

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